This invention relates to test fixtures, particularly on-board testers, for integrated circuit chips, such as a ball grid array (BGA) chip. The on-board tester (referred to herein as the xe2x80x9ctest fixturexe2x80x9d) includes an upper assembly and a lower assembly that attach through a circuit board mounted between the upper assembly and lower assembly. The circuit board contains the BGA chip to be tested and an electrical engagement between the test fixture and the BGA chip is achieved by rotational movement that linearly compresses probe test pins of the lower assembly against the BGA chip.
Testing of integrated circuits, such as those contained within ball grid array (BGA) packaging, is accomplished through the use of what is commonly referred to in the art as a test fixture. BGA test fixtures typically include a housing mounted to a load board which interfaces with the test electronics. The load board is generally a circuit board for transferring test signals from the integrated circuit in the BGA to the test electronics.
Previous methods of attaching the test fixture to the load board include through hole techniques and surface mounting techniques. In the surface mounting connection, the test fixture includes test pads which make contact with the solder balls on the bottom of the BGA as the BGA is compressed against the test pads to transfer the test signals to the load board. A problem associated with the surface mounting test fixture arrangement is that the solder balls on the bottom of the BGA can vary in height and good electrical contact between each solder ball and the test pad cannot always be assured. A second problem associated with surface mounting is that once the test pads become contaminated from the solder balls, the entire fixture assembly must be replaced.
Through hole techniques for connecting the fixture to the load board include holes drilled through the load board for the passage of spring loaded contact pins which contact the solder balls on the BGA and transfer the test signals to the load board through the contact between the test pins and the holes in the load board. A problem associated with the through hole fixture arrangement is that the test pins extending up through the load board could easily be bent or damaged which would negatively impact the test results. To avoid this problem, a receptacle can be positioned between the fixture and the load board to protect the test pins extending through the load board. The result of incorporating a receptacle requires the length of the test pins in the fixture to be increased which creates a problem for testing high speed integrated circuits. To address this problem spring probes have been incorporated which have a short travel length, however with short travel springs, the spring life is short requiring constant replacement. In addition, the use of spring probes in the fixture can create an impedance problem for the transfer of the test signal from the BGA to the load board.
Consequently, a need exists for a new test fixture for BGA packages which reduces the problems associated with prior art test fixtures. Particularly, a new test fixture that can be easily mounted on a circuit board and produce accurate results.
The present invention relates to an on-board tester (referred to herein as a xe2x80x9ctest fixturexe2x80x9d) for testing integrated circuit chips, particularly ball grid array (BGA) chips. The test fixture of the present invention eliminates many of the problems associated with presently available test fixtures, particularly the lack of control in mounting the chips to the test fixture, and the unpredictable testing results.
The present test fixture has an upper assembly and a lower assembly. A circuit board containing the BGA chip to be tested is mounted between the upper and lower assemblies. The lower assembly has guide pins extending toward the upper assembly which allows any circuit board having alignment holes that match the configuration of the guide pins to be mounted to the lower assembly. This makes the test fixture versatile as compared to many existing test fixtures which have a xe2x80x9cclamshellxe2x80x9d latching mechanism that will only allow a circuit board having exactly the same dimensional properties as the test fixture to be tested. Moreover, the present test fixture has a unique latching mechanism which uses rotational movement to latch and unlatch the test fixture. Particularly, a collet assembly is used which allows rotation of a shaft to compress other plates in the assembly so that the upper and lower assembly are properly secured together.
The test fixture of the present invention also provides increased testing accuracy by using rotational movement to secure the test pins of the test fixture to the BGA chip. The test fixture has a rotatable knob that is rotated to linearly draw the upper and lower assemblies together until a plurality of probe test pins have an effective electrical connection with the BGA chip. This controlled compression eliminates the problems of previous methods which tend to damage the test pins and provide unpredictable contact with the test pins, and thus produce unreliable results.